Computer-aided engineering technologies have previously been applied to simulate application of impact loads to vehicle bodies. These techniques are typically intended to replicate the type of crash testing that will eventually be performed on a completed automobile. Utilization of computer-aided engineering technologies, however, allows a simulated result of one or more of these tests to be considered during the design phase of an automobile, thus allowing automobile designs to be modified during a design phase to provide better structural performance during application of an impact load to the vehicle body.
In practice, these computer-aided engineering technologies include production of a three-dimensional model of the geometry and material properties of the automobile. Crash simulations are performed using these models, typically using the finite element method. The results of the simulation are typically rendered in the form of forces, stresses, and strain values that are generated within specific portions and features of the body of the automobile. These simulations also typically provide, as an end product, a visual representation of the deformations experienced within the automobile body during application of the impact loading.
The simulations are usually designed to correspond to tests that will be performed upon the completed vehicle. In the United States, these tests are specified by the Federal Motor Vehicle Safety Standards (FMVSS).
One particular area of interest regards the performance of the doors of the automobile during a side impact-type crash. In particular FMVSS 214 specifies a quasi-static door side intrusion test to determine the sufficiency of the strength of the door and the integrity of the mounting of the door with respect to the body of the vehicle. During a side impact type crash, the door structure of an automobile typically experiences intense rupture within its panels and the connections of its panels, such as spot welds, bolts, and hems. As a result of these ruptures, the manner in which the impact loading is distributed within the structure of the door changes significantly during the course of application of the impact force to the door due to fracture of the panels and their connections.
The door side intrusion test of FMVSS 214 subjects a door that is mounted to the body of a vehicle to an impact using an intruder that impacts the body at a low speed of about 0.2 in/sec in the physical test. The performance is simulated in the finite element analysis with a speed of 5 meters per second to keep the solution time practicable. The structural resistance offered by the door against intrusion by the intruder is measured to determine the initial, intermediate, and ultimate strength of the structure. During the testing, the integrity of the closure mountings of the door with respect to the vehicle body structure, such as at the latch and the hinges, is monitored to ensure that structural integrity of the closure mountings is maintained until the ultimate load is reached. Because the test causes severe deformation of the door structure and causes multiple ruptures of the panels and their connections, the sequence of these fractures is highly relevant to the overall performance of the door structure during the side intrusion testing.
During early phases of the side intrusion event, panels and associated components of the door structure buckle, and some fractures may occur at connections between components. When the ultimate strength of the structure is reached, the door structure has typically been subjected to widespread panel tear, spot weld rupture, hem separations, and potentially separation of the door at the latch and the hinge mountings. Of course, the structural performance of the door at its ultimate strength varies based on the geometry and layout of the door structure in terms of its cross members and reinforcements.
Although door side intrusion-type testing has previously been conducted using computer-aided engineering methods, success has been limited. Conventionally, non-linear finite element analysis solutions are utilized to simulate the structural performance of an automobile door during a side intrusion-type impact loading. In such an analysis, structural failures are judged after the fact, by applying rupture criteria to the mathematical model of the automobile door structure. This means that ruptures are not considered during the course of the analysis but only the most critical or ‘first’ failure is indicated over the analysis. Thus, the conventional non-linear finite element analysis modeling that is applied to door side intrusion modeling does not consider changes in the distribution of the impact loading within the door structure as a result of the structural failures that occur during the course of application of the impact loading.
It would be desirable to have a door side intrusion simulation method for simulating application of an impact load to an automobile door in which a changing impact load as a result of structural failures is properly accounted for.